I think this question is similar to "What if the moon stops orbiting the Earth?" It has devasting and interesting outcomes, but it's not gonna happen.

I would assume the body would just go into a coma. Spirits don't really enter bodies of people who astral project, and I've heard a few theories as to why, mostly involving the differences between the soul and astral bodies, or the silver thread, or just the awesome unstoppable-ness of the human spirit.

I think only the person born into a body has complete control over it. Besides, you've bonded spiritually with your body since birth. It's literally a part of you. I've even heard of people giving Gods and Lwa the boot.

This is a very complexed question.I've wondered that myself.Those who have split or multipul personalities,could this be the reason.Like you said coma,but what about someone who has that type of disability.I think you hit the jackpot with this.In the living we tend to get lost,confused,forgetful.So why could'nt it happen to your spirtual being.Oh my what if you have memory loss of any kind,like a disease,stroke,or a whack to the head.Would your spiritual being forget to.Wow this is a really good question.Thanks for sharing.

I've always wondered about if split personalities were more than one spirit living in the same body. Because one personality commits a crime, hides, and the other doesn't know a thing. It could be two spirits, one weaker, one stronger.